As always, WolframAlpha is your friend: http://www.wolframalpha.com/input/?i=3+millilight+seconds http://www.wolframalpha.com/input/?i=3+millilight+seconds 55

As always, WolframAlpha is your friend: http://www.wolframalpha.com/input/?i=3+millilight+seconds http://www.wolframalpha.com/input/?i=3+millilight+seconds 558.8 miles or 899.4 kilometers They even have "comparisons", e.g. for 30 millilight seconds: ~~ 1.4 x Amazon River length (~~ 6400 km )